Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate. The wastegate valve may be controlled based on operating conditions to achieve the desired boost. In one example, the wastegate valve may be an electronic wastegate controlled by an associated electric actuator. The electric actuator is driven to alter the wastegate position, thereby controlling the amount of gas reaching the turbine and achieving the desired boost. In some downsized engines, whose volumes have been reduced to improve fuel economy, a turbocharger is included to recover the loss in performance due to downsizing.
In some examples, an electric actuator is used to control the position of a wastegate valve. The electric actuator, for example, may be an electric motor which transmits a linear force to a rod. The rod may directly actuate the wastegate valve, or alternatively, the rod may be coupled to a rotating member which transmits rotational motion to the wastegate valve.
The inventors herein have recognized a problem with such approaches utilizing electric actuators to control the position of a wastegate valve. In downsized engines, loss of wastegate valve control due to a degraded actuator may cause insufficient boost to be delivered to the engine. In this case, the engine may not supply the desired level of torque and output. Thus, the degree of downsizing of the engine may be limited due to wastegate degradation concerns. For example, loss in wastegate valve control may cause insufficient boost to be delivered to an engine, particularly when the wastegate valve is pushed into a partially open position due to exhaust flow pressure and flow forces. In this case, the degraded actuator cannot supply sufficient closing force to the valve.
Systems and methods for compensating a degraded electric actuator operatively coupled to a wastegate valve are provided. For example, a method may include adjusting a wastegate actuator coupled to a wastegate valve in an engine exhaust to control an engine boost level of an engine, the adjustment based on a force supplied by a bias.
In one example, a spring is coupled to an electric wastegate actuator, the spring maintaining a wastegate valve in a closed position up to a threshold pressure. In an un-degraded operation, the electric actuator is moved toward an open position with a first current and moved toward a closed position with a second current, in addition to being biased toward the closed position via the spring.
In this way, by coupling a spring to an electric wastegate actuator and maintaining a wastegate valve in a closed position up to a threshold manifold pressure via the biasing spring force (e.g., spring pre-load), sufficient boost may be provided to an engine and desired engine output ensured even if the electric actuator has degraded. Further, due to the supply of closing force via the spring, the size of the electric actuator may be reduced, reducing power consumption. Downsized engines may also forego or reduce dimensioning to account for wastegate degradation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.